Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $167.39   6.754%   $178.6955   $178.70   $178.70   $178.70  
  Purchase #2 $225.37   10.661%   $249.3967   $249.40   $249.40   $249.40  
  Purchase #3 $50.92   5.589%   $53.7659   $53.77   $53.75   $53.80  
  Purchase #4 $86.75   5.334%   $91.3772   $91.38   $91.40   $91.40  
  Purchase #5 $164.71   8.425%   $178.5868   $178.59   $178.60   $178.60  
  Purchase #6 $240.71   9.134%   $262.6965   $262.70   $262.70   $262.70  
  Purchase #7 $216.29   10.129%   $238.198   $238.20   $238.20   $238.20  
  7 purchase totals = $1,152.14       $1,252.7166   $1,252.74   $1,252.75   $1,252.80